This invention relates, in general, to chemical vapor deposition of semiconductor wafers, and more particularly, to a method for introducing impurities into a carrier gas line going to a reaction chamber.
During the manufacture of semiconductor devices there is often the requirement for a dielectric layer such as a layer of SiO.sub.2, Si.sub.2 N.sub.3, or the like to provide electrical isolation. In some laser or LED structures manufactured with a multiplicity of layers of GaAs and AlGaAs it is desirable to have an insulating layer as a top layer covering the GaAs cap layer. Sources of gases to form these layers are typically connected to a manifold which controllably allocates the desired dopant or gas to the reaction chamber. It has been discovered that a semi-insulating layer can be obtained by incorporating small amounts of an oxygen containing species such as O.sub.2, H.sub.2 O, or the like into an AlGaAs layer. One way of getting the oxygen into the system is by feeding the oxygen or water vapor through a needle valve or mass flow controller into the gas carrier line going to the reaction chamber. However, flow volume changes are generally necessary when using the needle valve and it is extremely difficult to obtain reproducibly the required parts per million levels of impurities in the carrier gas.
Accordingly, it is an object of the present invention to provide an improved method for adding an impurity into a carrier gas line to a reaction chamber.
Another object of the present invention is to provide an improved method for obtaining semi-insulating layers in a semiconductor structure.
Yet another object of the present invention is to provide a method for using a permeable tube to add dopants into a semiconductor processing system.
A further object of the present invention is to provide a semi-insulating layer by adding oxygen to AlGaAs.